DEMO
An element becomes entries in a global matrix
Hover the triangular elements. The companion matrix highlights the degrees of freedom touched by each element and shows how shared nodes combine contributions.
Brighter means larger. K is symmetric, and dense only near the diagonal: neighbours in the mesh end up near each other in the matrix.
Model scope. Connectivity assembly uses illustrative local coefficients (2 on the diagonal and −0.85 off it). It shows sparsity and indexing, not the native BᵀDB elasticity matrix or its material-dependent values.